EXPRESS: Suspected pneumothorax ex vacuo associated with fibrotic pleurisy in a cat with idiopathic chylothorax

Case summary A 7-year-old mixed-breed cat was diagnosed with idiopathic chylothorax. Following left-sided thoracentesis, pneumothorax developed, and a thoracic drain was placed for intermittent pleural drainage. The cat subsequently underwent subtotal pericardiectomy via median sternotomy, with placement of a closed suction drain. Although the postoperative respiratory status was initially stable, pneumothorax recurred following the application of negative pressure through the thoracic drain. Continuous low-pressure aspiration using a closed suction system resulted in resolution of the pneumothorax, and the chylous pleural effusion gradually decreased. No recurrence of pneumothorax or chylothorax was observed at 773 days. Histopathological findings confirmed fibrotic pleurisy, and the overall clinical and imaging findings were consistent with a suspected non-expandable lung. The clinical course was considered consistent with pneumothorax ex vacuo as described in humans, highlighting the need to avoid excessive negative pressure during thoracic drainage in cats with suspected fibrotic pleurisy. Relevance and novel information This report highlights the potential for pneumothorax ex vacuo during thoracic drainage in cats with suspected fibrotic pleurisy, and emphasizes the importance of gentle, controlled pleural drainage.